Three distinct and different types of teaching improvement are identified and described. Type R (Remedial) consists of the detection and elimination of errors in teaching, such as in preparation or evaluation. Type F (Facilitative) emphasizes the use of appropriate general principles: use of objectives, frequent testing, knowledge of results, etc., to facilitate student learning. Type O (Optimizing) requires the use of a research orientation in order to determine the procedures and techniques which do, in fact, produce the highest level of student achievement. Several examples are given to illustrate the contention that procedures which are actually effective for type O improvement cannot be identified through theory or intuition, but can only be discovered by a systematic programme of introducing variations, gathering data, and evaluating the results.